The present invention relates to an economical high-voltage pulse power source of high performance for applying a steep pulse voltage to a load consisting of a resistive load or a corona discharge load and an electrostatic capacity connected in parallel thereto, such as load in electric dust collecting apparatus or ozonizer. The invention is also concerned with a pulse-charging type electric dust collecting apparatus equipped with said high-voltage pulse power source.
In the prior high-voltage pulse power sources for above-mentioned kinds of load, the common practice is that, after a pulse voltage-forming capacitor has been charged with a D.C. power source for charging, the capacitor is momentarily connected to the load to discharge via a high-voltage switch element, and a pulse high voltage resulting from CR attenuation is generated between both ends of the load. Because of the difference in D.C. voltage level between the high-voltage pulse power source and the load, it is usual in these cases to connect the power source with the load by means of a pulse transformer and a coupling capacitor. However, with this structure as such, said pulse voltage-forming capacitor is again charged to a high voltage by the D.C. charging power source after an ON action of said high-voltage switch element. As a result, the high-voltage switch element is reignited and a dynamic current flows from the charging power source to the load. Consequently, a periodic pulse voltage cannot be generated. To prevent this phenomenon, a method is devised that a high current-limiting resistance is interposed between the D.C. charging power source and the pulse voltage-forming capacitor for limiting the rate of recharging. Thus, the reset to OFF state of high-voltage switch element after ON action thereof is ensured by extinction. However, when a high current-limiting resistance sufficient to secure the reset to OFF state is employed, the drawback resides in that an excessive time is required to charge the pulse voltage-forming capacitor and a high frequency of pulse voltage cannot be obtained. Moreover, the power loss due to this current-limiting resistance is great and the power efficiency of high-voltage pulse power source is far lowered. This is another drawback. These drawbacks have prevented the method to be practised.
In the prior art, it is well known a "method of pulse-charging" wherein a periodic pulse high-voltage, in place of D.C. high-voltage, is impressed on the discharge electrode of electric dust collecting apparatus to enhance the performance of dust collecting. However, in all prior systems, the pulse high-voltage is superimposed on the existing D.C. high voltage of the discharge electrode. Accordingly, it is required that any coupling interface, such as pulse transformer, coupling capacitor and a combination thereof, is inserted between the output terminal of high-voltage pulse power source and the discharge electrode so that the D.C. continuity may be broken but any pulse voltage may be freely transferred. By this usual provision, the direct connection between the high-voltage pulse power source and the discharge electrode is avoided and the impression of D.C. high-voltage of discharge electrode onto the output side of high-voltage pulse power source can be prevented. However, as the electric dust collecting apparatus is scaled up, the required capacity of said coupling interface becomes very large. Thus, the cost of the construction remarkably increases. In addition, the power loss in the interface is increased excessively. As a result, the realisation of the pulse-charging method itself becomes scarcely practicable.